Upload a metallographic micrograph and measure grain size using the Heyn intercept method. Client-side processing — images never leave your browser.
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The most common source of error is incorrect pixels-per-micron calibration. If your micrograph has a scale bar, measure it in pixels and enter the known length. An incorrect calibration will systematically shift all grain size numbers — the intercept lengths scale linearly with the calibration factor.
ASTM E112 requires a minimum of 50 grain boundary intersections for a statistically reliable measurement. With fewer intercepts, the standard deviation of the grain size estimate becomes unacceptably large. Use multiple test lines across at least 3 fields of view to reach this threshold.
Faint or incomplete grain boundaries lead to missed intersections and overestimated grain size (lower G number). If boundaries are hard to see, the specimen likely needs re-etching. Nital for carbon steels, Kalling’s No. 2 for stainless steels, and Keller’s reagent for aluminum alloys are standard choices.
Avoid measuring only in regions that look “typical” by eye. ASTM E112 specifies random or systematic field selection to avoid sampling bias. If the microstructure is heterogeneous (e.g., banded or duplex grain size), report the range and consider ASTM E1181 for characterizing grain size distributions.
| G Number | Avg. Diameter (mm) | Grains / mm² |
|---|---|---|
| -3 | 1 | 1 |
| -2 | 0.75 | 2 |
| -1 | 0.5 | 4 |
| 0 | 0.36 | 8 |
| 1 | 0.25 | 16 |
| 2 | 0.18 | 32 |
| 3 | 0.125 | 64 |
| 4 | 0.091 | 128 |
| 5 | 0.062 | 256 |
| 6 | 0.044 | 512 |
| 7 | 0.031 | 1,024 |
| 8 | 0.022 | 2,048 |
| 9 | 0.016 | 4,096 |
| 10 | 0.011 | 8,192 |
| 11 | 0.008 | 16,384 |
| 12 | 0.006 | 32,768 |
| 13 | 0.004 | 65,536 |
| 14 | 0.003 | 131,072 |
Heyn linear intercept method per ASTM E112-13. User draws test lines on the uploaded micrograph; grain boundary intersections are counted to compute mean intercept length, which maps to the ASTM grain size number via the standard conversion formula: G = −6.6457 × (ℓ) − 3.298. All image processing uses the browser Canvas API — no server upload.
Last validated 2026-03-20. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience ASTM E112 Grain Size Analyzer (v1.0). ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/astm-e112-grain-size-analyzer
ASTM E112-13. Standard Test Methods for Determining Average Grain Size. ASTM International, West Conshohocken, PA. doi:10.1520/E0112-13R21
ASTM E112 (“Standard Test Methods for Determining Average Grain Size”) is the definitive standard for measuring grain size in metals and alloys. Grain size directly affects mechanical properties — yield strength, hardness, ductility, and fatigue resistance all depend on it. The Hall–Petch relationship predicts that finer grains produce stronger metals.
Materials scientists, quality control engineers, and metallurgists use grain size measurements for incoming inspection, process control, failure analysis, and compliance with specifications in aerospace (AMS), automotive (IATF 16949), and nuclear (ASME) industries.
The Heyn intercept method is the most objective of the three ASTM E112 approaches. A set of straight test lines of known total length is placed on the micrograph. Each grain boundary crossing is counted. The mean intercept length is:
where L is the total test line length (corrected for magnification) and N is the total number of boundary intersections. The ASTM grain size number G is then calculated from:
where ℓ is in millimeters. A higher G number means finer grains. Most engineering alloys fall between G = 1 (coarse) and G = 14 (ultrafine).
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